Quinacridone pigments in electrophotographic imaging

ABSTRACT

AN ELECTROPHOTOGRAPHIC METHOD WHICH EMPLOYS QUINACRIDONE PIGMENTS AS THE PHOTOCINDUCTOR IN THE IMAGING PLATE.

United States Patent US. Cl. 96- -1 PC 9 Claims ABSTRACT OF THE DISCLOSURE An electrophotographic method which employs quinacridone pigments as the photoconductor in the imaging plate.

This application is a continuation of application Ser. No. 469,143 filed July 2, 1965, now abandoned.

This invention relates to electrophotography and more particularly to a binder plate usable in electrophotography.

It is known that images may be formed and developed on the surface on certain photoconductive insulating materials by electrostatic means. The basic electrophotographic process, as taught by Carlson in US. Patent 2,297,691, involves uniformly charging a photoconductive insulating layer and then exposing the layer to a light-andshadow image which dissipates the charge on the portions of the layer which are exposed to light. The electrostatic latent image formed on the layer corresponds to the configuration of the light-and-shadow image. Alternatively, a latent electrostatic image may be formed on the plate by charging said plate in image configuration. This image is rendered visible by depositing on the imaged layer a finely divided developing material comprising a colorant called a toner and a toner carrier. The powdered developing ma terial will normally be attracted to those portions of the layer which retain a charge, thereby forming a powder image corresponding to the latent electrostatic image. Where the base sheet is relatively inexpensive, such as paper, the powder image may be fixed directly to the plate as by heat or solvent fusing. Alternatively, the powder image may be transferred to a sheet of receiving material, such as paper, and fixed thereon. The above general process is also described in US. Patents 2,357,809; 2,891,011; and 3,079,342.

The photoconductive insulating layer to be effective must be capable of holding an electrostatic charge in the dark and dissipating the charge to a conductive substrate when exposed to light. That various photoconductive insulating materials may be used in making electrophotographic plates is known. Suitable photoconductive insulating materials such as anthracene, sulfur, selenium or mixtures thereof have been disclosed by Carlson in US. Patent 2,297,691. These materials generally have sensitivity in the blue or near ultra-violet range, and all but selenium have a further limitation of being only slightly light-sensitive. For this reason, selenium has been the most commercially accepted material for use in electrophotographic plates. Vitreous selenium, however, while desirable in most aspects, suffers from serious limitations in that its spectral response is somewhat limited to the ultraviolet, blue and green regions of the spectrum and the preparation of vitreous selenium plates requires costly and complex procedures, such as vacuum evaporation. Also, vitreous selenium layers are only meta-stable in that they are readily recrystallized into inoperative crystalline forms at temperatures only slightly in excess of those prevailing in conventional electrophotographic copying machines. Further, selenium plates require the use of a separate conductive substrate layer, preferably with an additional barrier layer deposited thereon before deposition of the selenium photoconductor. Because of these economic and commercial considerations, there have been many recent efforts toward developing photoconductive insulating materials other than selenium for use in electrophotographic plates.

It has been proposed that various two-component materials be used in photoconductive insulating layers used in electrophotographic plates. These consist of a photoconductive insulating material in particulate form dispersed in an insulating binder. Where the particles consist of a photoconductive material comprising inorganic crystalline compounds containing a metallic ion, satisfactory photographic speed and spectral response for use in xerographic plates are obtained. However, these plates even when dye-sensitized generally have sensitivities much lower than selenium. These plates are generally considered to be non-reusable since it is necessary to use such high percentages of photoconductive pigment in order to attain adequate sensitivity that it is difficult to obtain smooth surfaces which lend themselves to efiicient toner transfer and subsequent cleaning prior to reuse. An additional drawback in the use of inorganic pigment-binder type plates is that they can be charged only be negative and not by positive corona discharge. This property makes them commercially undesirable since negative corona discharge generates much more ozone than positive corona discharge and is generally more difficult to control.

It has been further demonstrated that organic photoconductive dyes and a wide variety of polycyclic compounds may be used together with suitable resin materials to form photoconductive insulating layers useful in bindertype plates. These plates generally lack sensitivity levels necessary for use in conventional electrophotographic copying devices. In addition, these plates lack abrasion resistance and stability of operation, particularly at elevated temperatures.

In another type plate, inherently photoconductive polymers are used frequently in combination with sensitizing dyes or Lewis acids, to form photoconductive insulating layers. These polymeric organic photoconductor plates generally have the inherent disadvantages of high cost of manufacture, brittleness, and poor adhesion to supporting substrates. A number of these photoconductive insulating layers have thermal distortion properties which make them undesirable in an automatic electrophotographic apparatus which often includes powerful lamps and thermal fusing devices which tend to heat the electrophotographic plate.

Thus, there is a continuing need for improved photoconductive insulating materials from which stable, sensitive, and reusable electrophotographic plates can be made.

It is therefor an object of this invention to provide an electrophotographic plate devoid of the above-noted disadvantages.

Another object of this invention is to provide electrophotographic plates having sensitivities which extend over substantial portions of the visible spectrum.

Still another object of this invention is to provide a reuseable electrophotographic plate having a high overall sensitivity and high thermal stability when compared to present commercially available reuseable plates.

Yet another object of this invention is to provide a photoconductive insulating material suitable for use in electrophotographic plates in both single use and reusable systems.

Yet another object of this invention is to provide a photoconductive insulating layer for an electrophotographic plate which is substantially resistant to abrasion and has a relatively high distortion temperature.

Yet another further object of this invention is to provide an electrophotographic plate having a wide range of useful physical properties.

The foregoing objects and others are accomplished in accordance with this invention, fundamentally, by providing an electrophotographic plate having a novel photoconductive layer containing a quinacridone in'a resin binder.

The quinacridone-resin photoconductive layer may be deposited on any suitable supporting substrate, or may be cast as a self-supporting film. The plate may be over coated with any suitable material, if desired. The quinacridone-resin photoconductive layer may be used in the formation of multi-layer sandwich configurations adjacent a dielectric layer, similar to that shown by Golovin et al., in the publication entitled A New Electrophotographic Process, Eifected by Means of Combined Electret Layers Doklady. Akad. Nauk SSSR vol.'? 129, No. 5, pages 1008-1011, November-December 1959. It has been found that the percentage of quinacridone required to produce adequate sensitivity in a plate is very low. Because of this, the mechanical properties of the photoconductive layers are substantially determined by the properties of the binder. A wide variety of resin binders may be used in the present invention, varying from soft ther moplastics to hard cross-linked enamels. Thus, the physical properties of the final photoconductive layer may be varied over wide limits by selection of the appropriate resins to suit specific requirements. In this regard, these photoconductive layers are superior to the heretofore known binder suspensions of inorganic pigments which require a relatively high percentage of inorganic pigment such that the inorganic pigment used essentially controls the physical properties of the final photoconductive layer. Since the percentage of quinacridone pigment needed is relatively low, the photoconductive plate may have a very hard, very smooth surface. This eliminates many of the disadvantages of the prior pigment-binder plates which, because of the high proportions of pigment, had a very rough and abrasive surface.

Any suitable quinacridone, substituted or unsubstituted, in any suitable crystal form and in any suitable configuration may be used to prepare the photoconductive layer of the present invention. Quinacridones are known to exist in several inter-convertible crystal forms. Several of these different crystal forms and methods of preparing them are described in detail in U.S. Patents 2,844,484; 2,844,485; and 2,844,581. Quinacridones encompassed thereof. In addition, metal salts of quinacridones such as the barium salt of'2,9-dimethyl-3,IO-disulfo quinacridone may be used where suitable. For use in electrophotographic plates, the quinacridone may have other compositions added thereto to sensitize, enhance, synergize or otherwise modify its properties. Also, angular quinacridones, such as disclosed in U.S. Patent 2,830,990 may be used where suitable. The quinacridone may, where desired, be formed into solid solutions with'other compositions, disclosed in U.S. Patent 3,160,510.

Of the above quinacridones, unsubstituted quinacridone, 4,11 dimethyl quinacridone 2,9-dimethyl quinacridone and 4,11 dichloro quinacridone and mixtures thereof are preferred, since they produce the most desirable images, are highly photosensitive and are readily available.

Any suitableorganic binder resin may be used in combination with the quinacridones to prepare the photoconductive layer of this invention. In order to be useful the resin used in the present invention should be more resistive than about 10 and preferably more than 10 ohms per centimeter under the conditions of electrophotographic use. Typical resins include: thermoplastics including olefin polymers such as polyethylene and polypropylene; polymers derived from dienes such as polybutyldiene, polyisobutylene, and polychloroprene; vinyl and vinylidene polymers such as polystyrene, styreneacrylonitrile copolymers, acrylonitrile-butadiene-styrene terpolymers, polymethylmethacrylate, polyacrylates, polyacrylics, polyacrylonitrile, polyvinylacetate, polyvinyl alcohol, polyvinylchloride, polyvinylcarbazole, polyvinyl others, and polyvinyl ketones; fluorocarbon polymers such as polytetrafluoroethylene and polyvinylidene fluoride;

within this invention may be described as compositions having a structure which appears to be the condensation of a quinoline residue with an acridine residue, with two carbons of the condensation product oxidized to the quinone stage. As noted above, any suitable quinacridone may be used to prepare the photoconductive layer of the present invention. Typical quinacridones include:

Various quinacridones may be utilized alone or in combination with other compositions in any suitable mixture, dimer, trimer, oligomer, polymer, copolymer or mixtures heterochain thermoplastics such as polyamides, polyesters, polyurethanes, polypeptides, casein, polyglycols, polysulfides, and polycarbonates; and cellulosic polymers such as regenerated cellulose, cellulose acetate and cellulose nitrate. Also, thermosetting resins including phenolic resins; amino'resins such as urea-formaldehyde resins and melamine-formaldehyde resins; unsaturated polyester resins; epoxy resins, silicone polymers; alkyd resins and furan resins. Various copolymers and mixtures of the above-mentioned resins may be used where applicable. In addition, to the above-noted resins, any other suitable material may be used if desired.

The quinacridone compositions may be incorporated into the dissolved or melted binder-resin by any suitable means such as strong shear agitation, preferably with simultaneous grinding. Typical methods include ball milling, roller milling, sand milling, ultrasonic agitation, high speed blending and any combination of these methods. Any suitable ratio of pigment to resin may be used. Do a quinacridone-dry resin weight basis, the useful range extends from about 1:1 to about 1:40. Best results are obtained at, and therefore the preferred range is, from about 1:4 to about 1:10. Optimum results are obtained when the ratio is about 1:4. While highest photosensitivity is obtained at pigment-resin ratios of 1:1 to 1:4, at the higher concentrations of pigment dark conductivity increases. The optimum balance between sensitivity and dark decay occurs at a ratio of about 1:4. It should be noted that the proportion of photoconductor used in the preferred range lies substantially below that used in making heretofore known inorganic photoconductive binder plates. In these known plates, satisfactory electrophotographic sensitivity is attained only when the pigment-resin ratio is at least 2: 1.

The use in the present invention of lower pigment to resin ratios represents a highly desirable advantage over the prior art since a smaller amount of the'relatively expensive pigment component is required. Also, this permits very smooth adhesive coatings to be obtained because of the high binder content. The small proportion of added material has little effect on the physical properties of the binder resin. Thus, resins may be chosen having the desired softening range, smoothness, hardness, toughness, solvent resistance, or solubility and the like with assurance that the pigment will not affect these properties to any considerable extent.

When it is desired to coat the quinacridone-resin film on. a substrate, various supporting materials maybe used. Suitable materials for this purpose include alumie num. steel, brass, metallized or tin oxide coated glass, semi-conductive plastics and resins, paper and any other convenient material of bulk conductivity at the time of use ohms cm., or surface conductivity 10 ohms/ square. The pigment-resin-solvent slurry (or the pigmentresin-melt) may be applied to conductive substrates by any of .the well-known painting or coating methods, including spraying, flow-coating, knife coating, electro coating, Mayer bar draw-down, dip coating, reverse roll coating, etc. Spraying in an electric field may be preferred for smoothest finish and dip coating may be preferred for convenience in the laboratory. The setting, drying, and/ or curing steps for these plates are generally similar to those recommended for films of the particular binders as used for other painting applications. For example, quinacridone-epoxy plates may be cured by adding a crosslinking agent and stoving according to approximately about the same schedule as other baking enamels made with the same resins and similar pigments for paint application. A very desirable aspect of quinacridone compositions is that they are stable against chemical decomposition at the temperatures normally used for a wide variety of bake-on enamels, and therefore, may be incorporated in very hard glossy photoconductive coatings, having surfaces similar to'-automotive or kitchen appliance resin enamels.

The thickness of the quinacridone-binder films may be varied from about 1 to about 100 microns, depending upon the required characteristics. Self-supporting films, for example, cannot be conveniently manufactured in thicknesses thinner than about 10 microns, and are easiest to handle and use in the to 75 micron range. Coatings, on the other hand, are preferably formed in' the 5 to 30 micron range. For some compositions and purposes, it is desirable to provide a protective overcoating. This overcoating should usually not exceed the thickness of a photoconductive coating and preferably should be no more than A the thickness of said coating. Any suitable overcoating material may be used, such as nitrocellulose lacquer.

The following examples are given to more fully illustrate specific embodiments of the invention. These examples are given for illustrative purposes only and are not intended to be limiting on the scope of the invention. In the examples, all parts are by weight unless otherwise specified. v

* EXAMPLE I A xergoraphic plate is prepared by initially mixing about 6 parts Pliolite SSB, a styrene-butadiene copolymer resin available from Goodyear Tire and Rubber Company, about 43 parts xylene and about 1 part Monastral Red B 790 -D, a 2,9-dimethyl quinacridone available from E. I. du Pont de Nemours and Company. This mixture is put into a glass jar containing a quantity of A:

formed-on the plate is then developed by cascading pig mented electroscopic marking particles over the plate, by the process described, for example, in US. Pat. 2,618,- 551. The powder image developed on the plate is electrostatically transferred to a receiving sheet and heat fused thereon. The image on the receiving sheet is of good quality and corresponds to the contact exposed original. The electrical characteristics and photographic sensitivity of this pigment are indicated in Table I below.

EXAMPLE II A xerog raphic plate is prepared by initially mixing about 2 parts Silicone SR-82 a methyl-phenyl silicone resin available from General Electric Co., about 40 parts xylene, and about 1 part Monastral Red B. This plate is coated, cured, charged, exposed and developed as in Example I above. However, here the plate is positively charged to an initial potential of about 290 volts. The image resulting is of satisfactory quality. As indicated in Table I, the sensitivity of this plate is relatively low.

EXAMPLES III-IV Two xerographic plates are prepared by mixing about 1 part Vinylite VYNS, a copolymer of vinyl chloride and vinyl acetate available from Union Carbide Corporation, about 10 parts diethyl ketone and about 1 part Monastral Red B. The plate is coated, cured, charged, exposed and developed as in Example I above, however, in Example III, the plate is positively charged to a potential of 480 volts and, in Example IV, the plate is charged to a negative potential of :835 volts. The resulting image is of excellent quality. As shown by Table I, this plate has especially high sensitivity.

EXAMPLES V-VI Two xerographic plates are prepared by initially mixing about 1 part of Vinylite VYNS, about 10 parts diethyl ketone and about 1 part Monastral Rey Y (an unsubstituted quinacridoue pigment available from Du Pont). The plate is coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example V is charged to a positive potential of 530 volts and the'plate of Example VI is charged to a negative potential of 630 volts. Good images result. See Table I for results.

EXAMPLES VII-VIII A xerographic plate is prepared by initially mixing about 1 part Vinylite VYNS, about 10 parts diethyl ketone, and about 1 part Monastral Violet R, which is beinch steel balls and milled on a Red Devil Quickie Mill (Gardner Laboratories), for about /2 hourin order to obtain a homogeneous dispersion. After milling, the dispersion is applied to a sheet of 5 mil aluminium foil using a No. 36 wire draw-down rod. The coating is then forced air dried at about 1100 C. for about two hours. The plate is then charged to a positive potential of about 650 volts by means of corona discharge, as described, for example, in US. Pat. 2,777,957. The charged plate is then contact exposed for 15 seconds to a film positive by means of a tungsten lamp having a 3400 K. color temperature. The illumination level at the exposure plane is about 57 foot candles. The latent electrostatic image lieved to be a solid solution of quinacridone and 4,11- dichloroquinacridone, which is available from E. I. du Pont de Nemours & Co. The plate is coated, cured, charged, and developed as in Example I above. However, here the plate of Example VII is charged to a positive potential of 410 volts and the plate of Example VIII is charged to a negative potential of 605 volts. Excellent images are produced by these plates. As shown in Table I, these plates have especially high photgoraphic sensitivity.

EXAMPLES lX-X Two xerographic plates are prepared by initially mixing about parts of a 10 percent solution of polyvinyl carbazole in benzene, about 5 parts cyclohexanone, and about 1. part Monastral Red B. These plates are coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example [X is charged to a positive potential of about volts and the plate of Example X is charged to a negative potential of about 215 volts. Images of good quality are produced. For further results, see Table I.

EXAMPLES XI-XII Xerographic plates are prepared by initially mixing about 100 parts of a 10 percent polyvinyl carbazole solution in benzene, about parts cyclohexanoneand about 1 part Monastral Violet R. The plates are coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example XI is charged to a positive potential of about 150 volts and the plate of Example XII is charged to a negative potential of about 180 volts. Images of good quality result. For further result see Table I. 1

EXAMPLES XIII-XIV Xerographic plates are produced by initially mixing about 100 parts of a percent solution of polyvinyl carbazole in benzene, about 5 parts cyclohexanone and about 1 part Monastral Violet R. The plates arecoated, cured, charged, exposed and developed as in Example I above. The plate of Example XHI, however, is charged to a positive potential of about 205 volts and the plate of Example XIV is charged to'a negative potential of about 185 volts. Images ofgood quality result. For further results, see Table I.

EXAMPLES XV-XVI Xerographic plates are produced by initially .mixing about 100 parts of a' 10 percent solution of polyvinyl carbazole in benzene, about 5 parts cycl'ohexanone and about 1 part Mona'stral Red Y. Theplates are, coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example XV is charged to a positive initial potential of 265 volts, and that of Example XVI to a negative potential of 275 volts. As is seen from Table I, this pigment exhibits substantially equal sensitivity with potential of either polarity.

EXAMPLES XVII-XVIII Xerographic plates are prepared by initially mixing about 100 parts of a 10 percent solution of polyvinyl carbazole in benzene, about 5 parts cyclohexanone, about 1 part Monastral Scarlet (a quinacridone pigment available from Du Pont). The plates are coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example XVII is charged to a positive potential of about 260 volts and the plate of Example XVIII is charged to a negative potential of about 330 volts. The resulting images are of good quality. Forfurther results, see Table I. 1 I

EXAMPLES XIX-XX Xerographic plates are prepared by initially mixing about 100 parts of'a 10 percent solution of polyvinyl carbazole in benzene, about 5 parts cyclohexanone and about 1 part Monastral Red B. The plates are coated, cured, charged, exposed and-developed as in Example I above. However, here the plate of Example XIX is charged to a positive potential of 300 volts and .the plate of Example XX is charged me negative potential of about 360 volts. Images of excellent quality result. For further results, see Table I.

8 EXAMPLES xxnxxn H I about l0-parts polyvinyl carbazole, about 90 parts benzene and about 1 part Monastral Red B. The plates are coated, cured, charged, exposed and developed as in 'Example I above.'HOWever, the plate of Example XXI-is charged to a positive potential of-about 190 volts and the plate of Example XXII is charged to a negative initial potential of about 220 voltsfExcelle'nt images resultziFor further characteristics, see Table II 7 EXAMPLES XXIII-XXIV Xerographic plates are prepared by initially mixing about 10 parts polyvinyl carbazole, about '90 parts benzene and about 1 part Monastral Red B,;which had been solvent extracted for about. hours-with-acetone in'a Soxhlet extractor. The plates are coated, cured, charged, exposed and developed'as in Example I above. However, here the plate of Example XXIII is charged to, a-positive potential of about .195 volts and the plate of Example XXIV is charged to anegative potential of about 270 volts. The images resulting are of excellent quality. As shown by Table I, the sensitivity of the more highly purified pigment increases slightly over that of the .unpurified pigment as used in Examples XXIXXII.

EXAMPLES XXV-XXVI v Xerograpln'cv plates are; initially prepared by mixing about 10 parts polyvinyl ,carbazole, about parts benzene-and about 1 part Monastral Red B which had been solvent extracted and precipitated onice from a sulphuric acid solution. The plates are coated, cured, charged, ex posed and developed as in Example I above, except that the initial potential on the plates arepositive 90 volts and negative volts, respectively. Excellent images result, As can be seen from Tablel, the further purified pigment has still higher photographicsensitivity.

EXAMPLES xxvn-xxvnr Xerographic plates are prepared by initially mixing about 6 parts Lexan, a polycarbonate resin available from General Electric C0,, about parts dichloromethane and about 1 part Monastral RedB RT-790-D. To this mixture is added about 50, parts eyclohexanone. The plates are coated, cured, charged, and exposed as in Example I above,

except that'the plate of Example XXVII is charged to'a positive potential of about 720 volts and the plate of Ex ample XXVI II is charged to a negative potential of about 760 volts. Images of satisfactory quality, but with high background, result.

,.EXAMPLES XXIX-XXX TABLE I Light Dark Residual Ill mination discharge discharge potential level Sensitivity (volts! (volts/ after 15 .(tt.- (voltsl' sec.) sec.) seconds ,candles) to. see) 50 10 150 70 0. G I 23 13 100 56 0.2 395 t 25 I00 7 52.8 1,175 75 16 68.9. 66. 7 3. 8 50 11. Z 5. 6 53. 4 4. 1 35 11.2 4. 4 S6. 7 2. 5 25' 11. 2 7. 5 62.3 7.6 25 11.2 4.9 66. 7 3. 0 50 ll. 2 5. 7. 46.7 6.7 V 11. 2 3.5

TABLE IContinued Light Dark Residual Illumination discharge discharge potential level Sensitivity Initial (volts/ (volts/ after (ft.- (volts potential sec.) sec.) seconds candles) to. sec.

+265 26. 6 3.0 110 11. 2 2. 1 275 23. 7 3. 8 95 11. 2 1. 8 +260 62. 3 2. 8 30 11. 2 5. 3 330 93. 4 4. 9 45 11. 2 7. 9 +300 187. 0 5. 3 55 11. 2 16. 2 -360 147. 0 5. 9 50 11. 2 12. 6 +190 23. 0 Trace 70 1 23. 0 220 26. 7 2. 0 70 1 24. 7 +195 28. 6 1. 5 50 1 26. 9 270 33. 3 Trace 70 1 33. 3 +90 8. 9 0 50 0. 18 49. 4 95 9. 7 0 35 0. 18 53. 9 +720 136 0 320 60 2. 3 760 240 Trace 280 60 4. 0 +640 232 4. 180 60 3. 8 670 208 3. 2 200 60 3. 4

Nora-In the above table, sensitivity represents the initial discharge rate upon illumination in volts/foot candle seconds corrected for the rate of dark discharge.

Although specific components in proportions have been described in the above examples relating to the use of quinacridone pigments in xerographic plates, other suitable materials, as listed above, may be used with similar results. In addition, other materials may be added to the quinacridone pigment compositions or to the pigmentresin compositions to synergize, enhance, or otherwise modify their properties. The pigment compositions and/ or the pigment-resin compositions of this invention may be dye-sensitized, if desired, or may be mixed or otherwise combined with other photoconductors, both organic and inorganic.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure, These are intended to be included within the scope of this invention.

What is claimed is:

1. A process for forming a latent electrostatic charge pattern on the surface of a photoconductive insulating layer which comprises forming a uniform electrostatic charge on the surface of said photoconductive layer said layer comprising a mixture of resin binder and a photosensitive quinacridone pigment and exposing said uniformly charged layer to a pattern of activating electromagnetic radiation.

2. The process as disclosed in claim 1 wherein said pigment is selected from at least one member of the group consisting of 2,9-dimethyl quinacridone, 4,11-dimethyl quinacridone, and 4,11-dichloro quinacridone.

3. The process as disclosed in claim 1 wherein from about 1 to about 40 parts of said resin binder are mixed for every 1 part quinacridone pigment.

4. A method of forming a latent electrostatic image on the surface of an electrophotographic plate which comprises uniformly charging the surface of said plate with an electrostatic charge, said plate comprising a support substrate having fixed to the surface thereof a photoconductive insulating layer, said photoconductive layer comprising a mixing of a resinous binder and a photosensitive quinacridone pigment and exposing said charged plate to a pattern of activating electromagnetic radiation.

5. A method as disclosed in claim 4 further including the step of developing said charge pattern with electrically attractable marking particles.

6. The process as disclosed in claim 5 further including the steps of repeating the charging, exposing and developing steps at least more than once.

7. An electrophotographic process comprising electrostatically charging a electrophotographic plate in an image pattern, said plate comprising a support substrate having fixed to the surface thereof a photoconductive insulating layer comprising a mixture of a resin binder and a photosensitive quinacridone pigment and developing said pattern with electrically attractable marking particles.

8. An electrophotographic imaging process comprising forming an electrostatic latent image on the surface of a photoconductive plate comprising a support substrate having fixed to the surface thereof a photoconductive insulating material comprising a mixture of from about 1 to about 40 parts resin binder per one part photosensitive quinacridone pigment, and developing said latent image with electrically attractable marking particles.

9. The process as disclosed in claim 8 wherein said imaging and developing steps are repeated at least more than one time.

References Cited UNITED STATES PATENTS 2,844,485 7/ 8 Struve. 2,844,581 7/ 1958 Manger et al. 3,074,950 1/ 1963 Deuschel et al. 3,121,006 2/1964 Middleton et al. 3,264,298 8/1966 Beny et al. 3,384,565 5/1968 Tulagin et al.

FOREIGN PATENTS 911,477 ll/ 1962 England. 948,307 1/ 1964 England.

GEORGE F. LESMES, Primary Examiner I. C. COOPER III, Assistant Examiner U.S. Cl. X.R. 96l 5 

